Structure of Water Molecule Acid and Bases Worksheets

Water1. Draw the structure of a water molecule and describe its shape and using VSEPR
theory provide an explanation for the shape of the molecule.
2. Water is considered to be a polar molecule. Provide an explanation as to why water
molecules are considered to be polar. Your explanation should take into account
the nature of the covalent bonds in water, and its geometry.
3. Are all molecules polar? Carbon dioxide (CO2) is not a polar molecules. Why is
CO2 not a polar molecule even though the covalent bonds between C and O are
similar to those between O and H in water?
4. Water exhibits some unusual properties that other molecules of the same size do
not. List some of these properties, and provide an explanation as to why water
exhibits these properties.
5. Water is considered to be an essential component for the existence of life. What
properties of water make it suitable for sustaining life?
6. Some substances are very soluble in water while others are not. For example table
salt and ethanol is highly soluble in water, while compounds such as benzene and
decane have very low water solubility. Provide an explanation as to why we observe
these differences in solubility.
7. Water has a slight tendency to ionize. Pure water contains very small amounts of
hydronium and hydroxide ions. Write a chemical equation to describe ionization of
water.
Acids, Bases, and Buffers
1. Determine if the following statements are TRUE or FALSE. If the statement is FALSE
provide and explanation as to why.
a. An Arrhenius acid is a compound that increases the concentration of
hydrogen ions in solution.
b. A Bronsted-Lowry base is a compound that can donate hydrogen ions.
c. A Lewis acid is an election pair donor.
d. Water can act both an acid and a base and is known as an amphoteric
substance.
e. The conjugate base of the acid HSO4- is H2SO4.
f. In an acidic solution the the hydronium ion concentration is always larger
than the hydroxide ion concentration.
g. For a neutral solution the hydronium and hydroxide ion concentrations are
equal, and has a numerical value of 1 x 10-7 M.
h. The product of the hydronium and hydroxide ion concentrations is a constant
for all for all solutions and the numerical value of the product is 1 x 10 -14 M2.
i. Methanesulfonic acid, CH3SO3H, has a pKa of -7 while ethanol, CH3CH2OH,
has a pKa of 15.9. Ethanol is the stronger acid.
2. The pKa of Sulfuric acid is -3. What is the pH of a 0.1 M solution of sulfuric acid?
3. The pKa of Acetic acid is 4.7. What is the pH of a 0.1 M solution of acetic acid?
4. The pKa of Acetic acid is 4.7. Calculate the ratio of [base]/[acid] that would be
present in a solution of acetic acid maintained at pH 3.7.
5. Describe how you would prepare a acetate buffer at pH 5.5. Assume that you have
a 1 M stock solution of Acetic acid and a 1 M stock solution of Sodium Acetate.
Case 1
Acute Aspirin Overdose:
Relationship to the Blood Buffering System
Last modified 11 July 2012
Focus concept
Case The
Study:
response of the carbonic acid/bicarbonate buffering system to an overdose of aspirin is
examined.
Response of the Blood Buffering System to an Aspirin
Prerequisites
Overdose
C Principles of acids and bases, including pKa and the Henderson-Hasselbalch equation.
C
The carbonic
acid/bicarbonate blood buffering system.
Adapted from
http://www.providence.edu/chemistry/kcornely/Documents/
Case01_Acute_Aspirin_Overdose.pdf
Background
Youemergency
are an emergency
roomphysician
physician andand
you have
admitted
patient, a 23-year-old
You are an
room
youjust
have
justa admitted
a patient to the
female,
who
had
been
hospitalized
for
psychiatric
treatment
for
the
past
six months.
She was out
emergency room around 9 pm. The patient was disoriented,
had trouble
speaking,
on asuffering
day pass when
was brought
the emergency
room
around
pm. The patient was The patient
and was
fromshenausea
andtovomiting.
She
was
also9hyperventilating.
disoriented,
had trouble
was suffering
from nausea
and vomiting. She
was also
admitted
to taking
an speaking,
entire and
bottle
of aspirin
(acetylsalicylic
acid,
ASA), which
hyperventilating. The patient admitted to taking an entire bottle of aspirin, which contained 250
contained 250 tablets. The patient said that she took the tablets around 7 pm that
tablets. The patient said that she took the tablets around 7 pm that evening. You draw blood
evening.
You draw blood from the patient and the laboratory performs the analyses
from the patient and the laboratory performs the analyses shown in Table 1.1. The patient is
shown experiencing
in Table 1.1.
patient
is experiencing mild respiratory alkalosis.
mildThe
respiratory
alkalosis.
Table 1.1: Arterial blood gas concentration in patient
Patient, two hours after
aspirin ingestion
Patient, ten hours
after aspirin ingestion
Normal values
26 mm Hg
19 mm Hg
35-45 mm Hg
18 mM
21 mM
22-26 mM
113 mm Hg
143 mm Hg
75-100 mm Hg
pH
7.44
7.55
7.35-7.45
Blood salicylate
concentration, mg/dL
57
117
HCO3-
In the emergency room, the patient is given a stomach lavage with saline and two doses of
1. Once
ingested
ASA
is hydrolyzed,
the
stomach
acid,
well as
“ASA”
esterases in
activated
charcoal
to adsorb
the aspirin. by
Eight
hours
later, nausea
andas
vomiting
became
severe,
plasma,
salicylic
andsheacetic
acid.respiratory
Salicylicalkalosis,
acid is
pharmacologically
and her to
respiratory
rateacid
increased;
was in severe
andthe
further
treatment
active form of ASA. Write a balanced chemical equation for the hydrolysis of ASA.
The structure of aspirin is shown below: 1
2. Normal stomach pH is approximately 2.00. Calculate the % of salicylic acid that is
protonated, and the % that is deprotonated, at normal stomach pH. Assume that the
pKa of the carboxylic acid group of salicylic acid is 2.97.
3. In the event of an aspirin overdose emergency room treatment typically involves a
gastric lavage (i.e stomach pumping) at pH 8.5. Calculate the % of salicylic acid
that is protonated, and the % that is deprotonated at he pH of the stomach lavage.
4. Non-charged molecules are more readily absorbed through cell membrane than
are charged molecules. Using information from your answers to Q 3 and Q4, explain
how the gastric lavage may help to reduce aspirin absorption through the stomach.
5. Salicylates are known to act on the nervous system to stimulate respiration. Due to
this stimulatory effect patients with aspirin overdose exhibit hyperventilation. Explain
how salicylate induced hyperventilation could lead to:
a. the values of pO2 and pCO2 observed in the patient.
b. an increase in blood pH observed in the patient (think in terms of the
bicarbonate/carbonic acid buffer system.
6. Using the patient’s blood pH calculate the ratio of HCO3- to H2CO3 in the patient’s
blood 10 hours after ingestion of aspirin. How does this ratio compare to the ratio
that would be found in normal blood?
7. Would the H2CO3/HCO3- system work effectively as a buffer under the conditions
found in the patient 10 hours after aspirin ingestion? Explain.